The present invention generally refers to a method of welding mitered mating surfaces of frame sections of plastic material, adapted for use in windows and doors and having incorporated therein seals of heat weldable material e.g. thermoplastic material, extending over the entire frame section and composed of an attachment foot and at least one sealing lip. Further, the present invention relates to an apparatus for welding such mitered surfaces of frame sections.
In conventional welding processes, the mitered surfaces of the frame sections together with adjoining frame section zones are being heat-welded by a heated flat mirror until reaching welding temperature. Subsequently, the mirror is removed from the area of the mitered surfaces and the mitered mating surfaces of the frame sections are pressed together. This process results in the formation of welding beads which are made through a thorough mixture of seal material and frame material in the region of the mitered surfaces. This mixture fully negates or at least significantly deteriorates the elastic properties of the seals in the corner area.